1. Field of the Invention
The present invention relates to an optical communication method and apparatus, and more particularly to a method and apparatus for reducing system deterioration caused by polarization effects encountered in an optical communication system.
2. Description of the Related Art
Following the current trend of rapidly increasing a transfer rate and a transmission distance of an optical communication system, a variety of phenomena encountered by polarization effects have recently been proposed as principal factors in deterioration of system performance. For example, an optical signal-to-noise ratio (SNR) is degraded by a PDG (Polarization-Dependent Gain) and a PDL (Polarization-Dependent Loss) in a long-distance optical communication network using an EDFA (Erbium-Doped Fiber Amplifier), resulting in deterioration of system performance. The aforementioned problem can be considerably improved by reducing a DOP (Degree Of Polarization) of a transmission optical signal, such that there has generally been proposed a method for controlling a transmission end to perform a scrambling process on a signal's polarization. However, the polarization scrambling process allows the signal's polarization state to be uniformly distributed in the form of two orthogonal polarization states, resulting in the increased influence of a PMD (Polarization-Mode Dispersion). Therefore, not only the polarization scrambling process but also the appropriate PMD operation must be carried out to guarantee a performance of a high-speed and long-distance optical communication system.
In order to solve the aforementioned problems, a representative method for controlling a transmission end to apply a signal to either one of reference polarization axes of an optical path so as to compensate for the PMD has been described in PCT International Application Publication No. WO 01/65733, which is hereby incorporated by reference. However, the aforementioned PCT International Application WO 01/65733 has been designed to reduce only the influence of the PMD, such that it has difficulty in actively solving the optical signal deterioration problem caused by the polarization effects. In conclusion, if the influence of the PMD can be reduced and a signal's performance can be improved, the deterioration problem of the optical signal can also be effectively improved.